A-Level science command words: what describe, explain and evaluate want

Every exam question starts with an instruction, and that instruction decides what a full-mark answer looks like. Students often know the science but answer the wrong command word, and lose marks they should have banked.

Here are the command words you will meet most in A-Level Biology and Chemistry, and what each one wants.

State, give, name, identify

Short, factual answers. No explanation is needed and none is credited. "Name the bond that forms between amino acids" wants "peptide bond", not a paragraph about condensation reactions.

Describe

Say what happens or what something is like, without saying why. For a graph, describe the trend, any change in the trend, and quote values with units from the axes.

A common slip is drifting into explanation. If the question only says describe, the "because" part earns nothing, and it uses up time.

Explain

Say why or how. This is about cause and effect, and each link in the chain is usually its own mark. Good explanations use connecting words: "because", "so", "which means", "therefore".

For example, explaining why the rate of an enzyme reaction falls at high temperature needs the chain: bonds in the tertiary structure break, the active site changes shape, the substrate no longer fits, fewer enzyme-substrate complexes form.

Describe and explain

Both, in that order. Split your answer in two so neither half gets forgotten.

Suggest

Apply your knowledge to a situation you have not seen before. The mark scheme will accept a range of sensible answers, as long as they are grounded in real science. Do not leave it blank because it looks unfamiliar: that is the point of the question.

Compare

Give similarities or differences, and make each one a direct comparison. "Arteries have thick walls whereas veins have thin walls" is a comparison. Two separate descriptions are not.

Evaluate

Weigh up evidence or a claim. Give points for and against, then reach a conclusion that is supported by what you have said. Evaluation questions often lose marks because the conclusion is missing.

Calculate

Work out a numerical answer. Always show your working, give units, and match the number of significant figures to the data. Working shown can earn marks even if the final answer is wrong.

Draw, sketch, complete

A diagram or graph. Sketches need the right shape and labelled axes, but not exact values. Drawings need care: in Chemistry mechanisms, every curly arrow, dipole and lone pair counts. Our guide to A-Level Chemistry mechanisms goes through those mark points.

Justify

Give evidence or reasons for an answer or decision, usually from data in the question. Quote the data.

Putting it into practice

Before you start writing, underline the command word and count the marks. Then plan that many separate points of the right kind.

The fastest way to get used to this is by answering questions and marking them against the scheme. Every question on ExamKata shows the full mark scheme after you answer, and our guide to where students lose marks in A-Level Biology covers the most common slips.